Error building docker with Unreal Engine. Error shown "Error: 'EPIC_TOKEN' parameter is mandatory".

[JesusAnaya]

Setup

• CARLA version: 0.9.16 (branches ue4-dev)
• Platform: Ubuntu 22.04 LTS (kernel 6.8.0-101-generic)
• Python version: 3.10
• GPU: NVIDIA GeForce RTX 5070 Ti
• GPU Drivers: 590.48.01

Describe the bug

The monolith Docker build fails because the EPIC_USER and EPIC_TOKEN variables passed via CLI arguments (--epic-user, --epic-token) are not exported as environment variables before being referenced by Docker's --secret id=...,env=... syntax in build.sh.

Docker's --secret id=epic_token,env=EPIC_TOKEN reads from the process environment, but the CLI argument parsing in build.sh only assigns local shell variables (EPIC_TOKEN="$2"). Since these are never exported, Docker mounts empty secret files, causing build_ue4.sh to fail with Error: 'EPIC_TOKEN' parameter is mandatory.

The .env file code path works correctly because it uses export, but the CLI argument path does not.

Steps to reproduce

1. Clone the CARLA repository and checkout ue4-dev (or ue5-dev).

2. Run the monolith Docker build with CLI credentials:

./Util/Docker/build.sh --monolith --branch ue4-dev --epic-user=<USER> --epic-token=<TOKEN>

3. The build fails at the RUN --mount=type=secret step with:
   Error: EPIC_TOKEN parameter is mandatory

Expected behavior

The Docker build should correctly pass the EPIC_USER and EPIC_TOKEN values as secrets to the build container, regardless of whether they are provided via CLI arguments or a .env file.

Logs

[monolith 1/7] RUN --mount=type=secret,id=epic_user,uid=1000 \
    --mount=type=secret,id=epic_token,uid=1000 \
    bash /build_scripts/build_ue4.sh \
      --ue4-root /workspaces/unreal-egine \
      --epic-user $(cat /run/secrets/epic_user) \
      --epic-token $(cat /run/secrets/epic_token):
0.352 Error: 'EPIC_TOKEN' parameter is mandatory
------
Development.Dockerfile:86
--------------------
  85 |     ENV UE4_ROOT="/workspaces/unreal-egine"
  86 | >>> RUN --mount=type=secret,id=epic_user,uid=${UID} \
  87 | >>>     --mount=type=secret,id=epic_token,uid=${UID} \
  88 | >>>     bash /build_scripts/build_ue4.sh \
  89 | >>>       --ue4-root ${UE4_ROOT} \
  90 | >>>       --epic-user $(cat /run/secrets/epic_user) \
  91 | >>>       --epic-token $(cat /run/secrets/epic_token)
  92 |     
--------------------
ERROR: failed to build: failed to solve: process "/bin/sh -c bash /build_scripts/build_ue4.sh \
      --ue4-root ${UE4_ROOT} \
      --epic-user $(cat /run/secrets/epic_user) \
      --epic-token $(cat /run/secrets/epic_token)" did not complete successfully: exit code: 1

Scripts

The fix is to add export for both variables in Util/Docker/build.sh before the docker build command in the monolith section (after the empty-check, before the docker build call):

export EPIC_USER
export EPIC_TOKEN

Screenshots

N/A

Additional context

The root cause is in Util/Docker/build.sh lines 152–170. The CLI argument parsing (lines 91–96) assigns EPIC_USER and EPIC_TOKEN as local shell variables. The .env loading path (lines 147–150) correctly uses export, so credentials from a .env file work. However, when credentials are provided via --epic-user and --epic-token flags, Docker's --secret id=epic_user,env=EPIC_USER cannot read them because they are not in the environment.